Wheelchairs have become more portable and lightweight over the years to meet the needs of the active lives of their users. Portability has been improved by providing for so-called “folding” frame wheelchairs, which increase wheelchair portability over rigid or non-folding frame wheelchairs. One of the most popular approaches to providing a foldable or collapsible wheelchair is to couple the side frames of the chair together by a cross-bracing assembly in which the cross-bracing members, which are almost always tubes, are pivotally coupled together proximate their midpoints in an “X” shape. The X-tubes of the cross-bracing assembly are also pivoted at their ends to the top and bottom members of the side frame assemblies so that the X-tubes can pivot like a pair of scissors and bring the wheelchair side frames together in a compact configuration. U.S. Pat. Nos. 4,989,890, 4,861,056, 5,915,709, 5,328,183 and 5,253,886 are all typical examples of X-tube cross-bracing assemblies which are employed to allow movement of the side frames of the wheelchair to a folded or collapsed position. There are many other examples in the patent literature of X-tube folding wheelchair frames.
Several problems have bee encountered in connection with X-tube folding wheelchair designs. More particularly, the pivotal coupling of the cross-bracing tubes or members causes arcuate movement of the side frames, which in turn, forces tilting or splaying of the side frames during movement. If too much tilting (usually an outward splaying of the top of the side frames) occurs, the backrest upholstery mounted between the side frames is strained as the side frames are forced outwardly, and the upholstery can bind and stop folding of the X-tube frame assembly, preventing it from reaching the fully deployed or open position. This problem is often overcome by providing backrest upholstery which is relatively loose so as not to bind the X-tube frame assembly as it pivots in a scissors-like action. Loose backrest upholstery, however, has the substantial disadvantage of being very poor for user posture and positioning, and therefore, employing loose backrest upholstery is not a good “solution” to accommodating the arcuate movement of the side frames induced by X-tube cross bracketing assembly during folding and unfolding.
An additional problem in conventional X-tube folding wheelchairs is that seat rails or tubes are provided on the upper ends of the X-tubes of the cross-bracing assembly. These seat rails typically carry sling seat upholstery that has a transverse length dimension across the chair such that the sling seat goes into tension as the chair folds open to the fully deployed position. The tension of the seat upholstery maintains a pre-load on the folding X-tube cross-bracing assembly, which increases the stability and rigidity of the folding chair when it is in the deployed condition. While this technique for rigidifying the folding wheelchair frame is initially relatively effective, sling seat upholstery typically will stretch over time, and the pre-loading effect will be reduced or even eliminated.
Most typically, the seat rails carried by the upper ends of the X-tubes of the cross-bracing folding assembly fold down to a position superimposed over the upper frame member or tube of the side frames, as for example, can be seen in the assemblies of U.S. Pat. Nos. 4,989,890 and 4,861,056. This over and under design, however, results in a higher positioning of the seat upholstery and some additional weight in the overall wheelchair frame due to lengthier cross-bracing X-tubes which are required. Moreover, positioning the seat rails carried by the X-tubes over the uppermost side frame tubes interferes with the ability to have the backrest upholstery supporting frame members fold or pivot downwardly over the seat side frames to further reduce the bulk of the wheelchair.
Folding wheelchairs have been developed, however, that employ X-tube cross-bracing frame assemblies and seat upholstery supporting rails that fold to a side-by-side position in relation to the top side frame member instead of the over and under configuration set forth above. Such prior art side-by-side folding wheelchair frame assemblies are commercially available under the trademark STAR OX, through a Japanese manufacturer, and the trademark TI SPORTS, through a United States manufacturer. These designs enable X-tube folding wheelchairs to be lower and somewhat lighter, but again the folding linkage forces arcuate motion of the side frames.
Various attempts have been made to overcome the disadvantages which are encountered in connection with X-tube folding wheelchair assemblies so as to eliminate binding, reduce the forces required to open and close the chair and make the opening and closing more smooth and uniform in its operation.
One approach to solving these problems has been to provide vertically extensible frame members in the side frames of the wheelchair in order to try to accommodate folding without binding. Typical of this approach are the frame assemblies shown in U.S. Pat. Nos. 4,042,250, 4,542,918 and 5,253,886. In U.S. Pat. No. 4,042,250 to Rodaway, for example, a series of vertically telescoping side frame members have been employed. This approach, however, is relatively complex and requires numerous parts which must be telescoped and slid vertically together over substantial distances. U.S. Pat. No. 4,542,918 to Singleton is similar in its approach to the patent to Rodaway in that there are vertically telescoped side frame tubes that attempt to accommodate the scissors action of the X-tube cross-bracing frame members. This approach is also taken in U.S. Pat. No. 5,253,886 to Weege.
Another approach was taken in the frame assembly of U.S. Pat. No. 4,682,783 to Kuschall. The cross-bracing assembly that couples the side frames together has been extensively modified, and a second pivoting cross-bracing frame added. In U.S. Pat. No. 6,572,133 to Stevens, a complex cross-bracing assembly is provided in which the components scissor in a fore-and-aft direction to accommodate frame folding, rather than having the X-tubes oriented for scissoring in a vertical direction. The complexity of this solution and its attendant weight are substantial.
In my U.S. Pat. No. 6,241,275, hinged cross-bracing links are employed to enable folding, and in U.S. Pat. No. 5,328,183 to Counts, the X-tubes are pivotally coupled at their upper ends to fixed length links that also receive pins so as to limit X-tube pivoting and support the seat assembly in the open or deployed position.
Accordingly, it is an object of the present invention to provide a foldable wheelchair, a wheelchair frame assembly and a method which do not force the side frames to fold in an unparallel manner, and accordingly, which have smoother folding characteristics that eliminate binding of the X-tube cross-bracing frame members by the upholstery during folding.
Another object of the present invention is to provide an improved wheelchair folding mechanism and method which improves the overall rigidity of the wheelchair frame and eliminates the dependence on tensioning of the upholstery to achieve frame rigidity.
Another object of the present invention is to provide a foldable wheelchair, wheelchair frame assembly and method which eliminate the need to employ slack backrest upholstery in order to accommodate folding and unfolding.
Still a further object of the present invention is to provide a foldable wheelchair, foldable wheelchair frame assembly and method which reduce the weight and size of the wheelchair frame, which are economical to manufacture and which accommodate frame size modifications, all while having an overall aesthetic appearance.
The foldable wheelchair, wheelchair frame assembly, and the method of the present invention, have other objects and features of advantage which will become apparent from, or are set forth in more detail in, the accompanying drawing and the following Best Mode of Carrying Our the Invention.